Search

Two-dimensional (2D) materials have driven great interest due to a large specific surface area to volume ratio and adjustable surface behaviors, which show huge potentials for enhancing the activity of energy conversion and property optimization. In order to regulate the physicochemical properties of photocatalyst for water splitting reaction, defect engineering on 2D materials have drawn great attention. Meanwhile, a widely used strategy to improve the H 2 evolution rate kinetics has been achieved. In this paper, we prepared AgBr/g-C 3 N 4 catalyst by chemical precipitation. The obtained photocatalyst shows a unique charge transfer pathway. In addition, a deep understanding of the proton shuttle during H 2 evolution reactions can offer profound opinion into heterostructure construction and property optimization. It is found that the enhanced performance is correlated to the superiority of the S-scheme heterojunction and defect engineering on graphitic carbon nitride 2D materials. This work offers a novel method for improving efficiency in terms of energy conversion and property optimization. [Display omitted] • Surface nitrogen vacancy is instrumental in the chemisorption and activation of H 2 O. • S-scheme band of AgBr/g-C 3 N 4 is conjectured by the experiments and DFT calculations. • The prolonged photocarrier lifetime has increased H 2 production. • The results of XPS are consistent with the mechanism of S-scheme heterojunction. [ABSTRACT FROM AUTHOR]

The unsaturated edge Ag introduced on the surface of photocatalysts plays an important role in boosting photo-excited electrons for the photoreduction H 2 O reaction. However, a moderate and tractable strategy to efficiently expose edge Ag remains an enormous challenge. For this purpose, a core skeleton with 'Ag conductive nanosphere array' inside and a two-dimensional sheet structure with g-C 3 N 4 layer outside are formed. The introduction of Ag nanospheres into g-C 3 N 4 not only enlarges the distance between g-C 3 N 4 nanolayers, but also increases the exposure of Ag nanospheres. When Ag intimately contacts with g-C 3 N 4 , the electrons of g-C 3 N 4 voluntarily flow to the Ag. Consequently, a built-in electric field (IEF) has been formed at interface of Ag@g-C 3 N 4 heterojunction, which prevents the continuous flow of electrons from g-C 3 N 4 to Ag. Under irradiation, the e− accumulated in Ag tend to recombine with the h+ in the valence band of g-C 3 N 4 which is driven by Coulomb interaction and IEF. Ag nanospheres are fabricated as a co-catalyst to decorate the g-C 3 N 4 nanolayer, which hinder the conglomeration of g-C 3 N 4 nanolayers. Moreover, Ag@g-C 3 N 4 heterojunction provides polyunsaturated edge Ag as active sites, inducing prolonged lifetime of photogenerated electrons and formed the unique charge transfer channels. In addition, abundant nitrogen vacancies are formed, which strengthens the chemisorption of H 2 O. As a result, supreme Ag@g-C 3 N 4 realizes a high H 2 evolution of 312.5 μmol and preserves a good sustainability. This paper emphasizes the importance of unique electron transfer pathway and chemisorption of water for photoreduction H 2 O. [Display omitted] • Band structure of Ag@g-C 3 N 4 is conjectured by the experiments and DFT calculations. • Surface nitrogen vacancy and prolonged photocarrier lifetime has improved H 2 evolution. • Surface nitrogen vacancy is responsible for the chemisorption and activation of H 2 O. [ABSTRACT FROM AUTHOR]

Highlights: The porous structure and interconnected conductive pathways accommodate a large amount of iodine, entrap polyiodides and guarantee its efficient utilization. While the Fe single atom catalyst efficiently catalyzes the iodine/polyiodide conversion. With "confinement-catalysis" host, the ZnǀǀI2 battery delivers a high capacity of 188.2 mAh g−1 at 0.3 A g−1, excellent rate capability with a capacity of 139.6 mAh g−1 at 15 A g−1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Rechargeable aqueous zinc iodine (ZnǀǀI2) batteries have been promising energy storage technologies due to low-cost position and constitutional safety of zinc anode, iodine cathode and aqueous electrolytes. Whereas, on one hand, the low-fraction utilization of electrochemically inert host causes severe shuttle of soluble polyiodides, deficient iodine utilization and sluggish reaction kinetics. On the other hand, the usage of high mass polar electrocatalysts occupies mass and volume of electrode materials and sacrifices device-level energy density. Here, we propose a "confinement-catalysis" host composed of Fe single atom catalyst embedding inside ordered mesoporous carbon host, which can effectively confine and catalytically convert I2/I− couple and polyiodide intermediates. Consequently, the cathode enables the high capacity of 188.2 mAh g−1 at 0.3 A g−1, excellent rate capability with a capacity of 139.6 mAh g−1 delivered at high current density of 15 A g−1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Furthermore, the electrocatalytic host can also accelerate the I + ↔ I 2 conversion. The greatly improved electrochemical performance originates from the modulation of physicochemical confinement and the decrease of energy barrier for reversible I−/I2 and I2/I+ couples, and polyiodide intermediates conversions. [ABSTRACT FROM AUTHOR]

[Display omitted] Template is frequently studied as a structure-directing agent to tune the nanomorphology of photocatalysts. However, the influences of template on the polymerization of precursors and compositions of the resulting samples are rarely considered. Herein, a biomass carbon-modified graphitic carbon nitride (CCNx) with a thin-layer morphology is synthesized via one-pot surface-assisted polymerization of melamine precursor on organic yeast. The formation of the hydrogen bond between melamine and yeast induces a strong interfacial confinement, giving rise to small-sized CCNx. In addition, the carbon materials derived from yeast dramatically broaden n → π* visible light harvesting, improve electron delocalization, and greatly enhance charge carrier separation. The optimized CCNx presents a much higher photocatalytic hydrogen production rate of 2704 μmol g-1h−1 under visible light irradiation (λ ≥ 420 nm), which is nearly 11-fold that of its pristine counterpart. This work realizes the synergistic effect between morphology tunning and composition tailoring by using biomass template, which shows a great potential in developing efficient metal-free photocatalysts. [ABSTRACT FROM AUTHOR]

Lead-free relaxor ferroelectric (RFE) ceramics find application in a broad range of technological devices due to their large electrostrain. But few lead-free ceramics show electrostrain values of more than 1 %. Here, an extraordinary strategy to obtain giant electrostrain by manipulating defect dipoles in (Bi, Na)TiO 3 -BaTiO 3 -based RFE ceramics is developed, achieving a high electro-induced strain value of 1.68 %, with a corresponding effective piezoelectric coefficient (d * 33) of 1965 pm/V. Furthermore, the effect of defect dipoles on RFE ceramics is discussed. The defects are pinned after poling, forming defect dipoles polarization (P d) oriented along or close to the poling direction. P d significantly promotes the transformation of polar nano regions to ferroelectric domains during strain-electric field (S - E) cycles, resulting in ultra-high electrostrain. This work proposes a detailed mechanism considering defect dipoles coupling in RFE ceramics and provides a promising paradigm for achieving high electrostrain, which could be applied in designing a wide range of functional ceramics. [ABSTRACT FROM AUTHOR]

Hydrogen energy, as one clean energy, is one of the important ways to decarbonize in the future. The advancement of doping and constructing defect engineering in graphitic carbon nitride (g-C 3 N 4) show promise for artificial photosynthesis for H 2 evolution using solar energy. Unfortunately, it is still difficult to generate g-C 3 N 4 that has been co-modified by doping and defect and investigate their synergistic effects. In this study, potassium thioacetate was used first-time as a potassium source and dehydrogenation agent to prepare g-C 3 N 4 decorated by K+ ions and cyano groups with enhanced H 2 evolution by a one-step method in an air atmosphere. The presence of K+ ions can increase the density of electron clouds in the delocalized π bond of the heptazine ring. The cyano group may successfully delocalize the solitary valence electrons in conjugated heterocycles since it is a potent electron-withdrawing group. These outcomes allow the modified catalysts to achieve improved H 2 evolution activity, reduced interfacial transfer resistance, and increased light absorption and photocurrent. Finally, K(0.05)-CN's photocatalytic hydrogen evolution rate (HER) rose to 1319 μmol h−1 g−1, which is five-fold better than that of CN, and the normalized HER reached 118 μmol h−1 m−2, which was much higher than other reports. This research not only offers a fresh approach to creating photocatalysts with good H 2 evolution efficiency but also advances a deep understanding of how structural defects and alkali metal doping affect photocatalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface nitrogen vacancy is instrumental in the chemisorption and activation of H 2 O. • Surface nitrogen vacancy and extended photocarrier lifetime has improved H 2 production. • S-scheme band of AgI/g-C 3 N 4 is conjectured by the experiments and DFT calculations. AgI/g-C 3 N 4 S-scheme heterojunction with a unique electron transfer pathway was developed as a catalyst for H 2 evolution. We discussed the behavior of chemisorption and photoexcited charge carriers in photocatalytic reduction on the S-scheme AgI/g-C 3 N 4 heterojunction. It was demonstrated that the path of charge transfer mediated by S-scheme AgI/g-C 3 N 4 heterojunction was favorable for the improvement of electron utilization in photocatalysis. The advantage of S-scheme heterojunction was that the holes in the valence band (VB) of g-C 3 N 4 could recombine with the electrons in the conduction band (CB) of AgI due to the built-in electric field. Electrons on the CB of g-C 3 N 4 and holes on the VB of AgI were preserved for further photocatalytic reaction. Therefore, a distinctive electron transfer pathway was introduced in the S-scheme heterojunction. In addition, the lifetime of charge carriers was prolonged, and the reduced ability of electrons was increased as compared to reference g-C 3 N 4. It not only decreased the energy required for electron excitation, but also reduced the energy consumption for the charge transfer. This paper provided a new strategy to improve the utilization of photogenerated electrons and chemisorption of water for photocatalytic H 2 O splitting. [ABSTRACT FROM AUTHOR]

One of the most important methods for modifying semiconductors is defect engineering, but only the right quantity of defects in the right chemical environment can produce desirable results. Heat treatment processes associated with g-C3N4 are occasionally carried out in N2 atmosphere, however, the catalytic performance of g-C3N4 produced by direct condensation of only nitrogen-rich precursors in N2 atmosphere is often unsatisfactory. This is typically attributed to the introduction of numerous defects, but the actual relationship between the formation of defects and the N2 atmosphere is rarely explained, and the resulting quantity of defects is difficult to control. We propose that the melam to melem transition is restricted due to the lack of O2 during the heat treatment of the nitrogen-rich precursor of g-C3N4 in N2 atmosphere, which leads to a substantial quantity of defects in the synthesized g-C3N4. To enhance its photocatalytic property, we propose a method to reduce the quantity of defects due to calcinating in N2 atmosphere by protonating the precursor in a way that increases the polymerization of the product. The test analysis indicated that only a moderate quantity of defects that contribute to electron excitation and enhance the separation efficiency and density of photogenerated carriers were retained, and the hydrogen evolution performance of the prepared catalyst was significantly improved. [ABSTRACT FROM AUTHOR]

Lead-free ferroelectric ceramics have aroused widespread concerns, due to their properties of rapid charge/discharge and electric-induced strain without harming the environment. However, compared with thin-film capacitors, ceramics have a larger energy loss. In addition, the large time lag between electric field and strain also reduces its accuracy as an actuator. Therefore, the relaxor ternary solid solution (BaTiO 3 –Bi 0.48 Na 0.48 La 0.03 TiO 3 –NaNbO 3) was constructed in this work, aiming to obtain large energy storage efficiency and low time delay. The strategy and optimization aim to improve the relaxation degree and reduce the maximum permittivity temperature to room temperature, building a special crossover region where high and low dynamic polar nano regions co-existence. Thus a recoverable energy density of 1.24 J/cm3 under a low electric field (135 kV/cm) and a high energy storage efficiency (96%) are obtained and low hysteresis electrostriction with a large electrostriction coefficient (Q 33 = 0.0367 m4/C2) is also achieved in this system. This work suggests that this system can be considered promising materials as high-efficiency capacitors and high-precision actuators. It also attracts interest in the basic research on the dynamic changes of polar nano regions. [ABSTRACT FROM AUTHOR]

Tribismuth titanium niobium oxide (B 3 TiNbO 9 , BTNO) is one of the Aurivillius phases with the highest Curie temperature (T c), but its piezoelectric coefficient (d 33) is poor. When x = 0.045, high-temperature piezoelectric ceramics with d 33 of 11.9 pC/N and T c of 916.7 °C were prepared by (Mn 1/3 Ta 2/3)(4+ ω)+ modification of Ti4+ at B-site of Bi 2.99 (Li 0.5 Sm 0.5) 0.01 Ti 1- x (Mn 1/3 Ta 2/3) x NbO 9. The substitution will aggravate the distortion of BO6 octahedron due to the displacement of oxygen ions. The existence of Mn3+ in the dopant will act as an oxygen vacancy trap and then increase the resistivity. As a result, BTNO ceramics have enhanced piezoelectric properties as well as temperature and cycle stability. This work provides a theoretical basis for better high-temperature piezoelectric properties of A/B co-doped Aurivillius phase ceramics in the future. [ABSTRACT FROM AUTHOR]

Lead-free relaxor ferroelectric ceramics are attracting attention due to their fast charge/discharge and environmentally friendly properties. In this work, the bismuth sodium titanate-barium titanate-barium zirconate titanate [(0.94Bi 0 · 51 Na 0 · 47 TiO 3 -0.06BaTiO 3) -x BaZr 0.3 Ti 0 · 7 O 3 , abbreviated as BNBT-100 x BZT] relaxor ferroelectric ceramics were synthesized by the solid-state reaction technique. The microstructure, energy storage properties, and conductivity mechanism of BNBT-100 x BZT were analyzed as the barium zirconate titanate doping content changed. All BNBT-100 x BZT have a single perovskite structure by XRD. The BNBT-5BZT ceramics was found to be tetragonal by Rietveld refinement. Moreover, the doping of BZT is beneficial to optimize the breakdown strength (BDS). Owing to the higher BDS, an effective energy storage density of 1.457 J/cm3 was obtained under 122 kV/cm in BNBT-5BZT with an energy storage efficiency (η) of 81.9%. In addition, BNBT-5BZT has outstanding temperature and cycling stability. The results indicate that BNBT-5BZT ceramics is excellent candidates for energy storage devices. A new relaxor ferroelectric bismuth sodium titanate-barium titanate-barium zirconate titanate synthesized with a tetragonal phase shows an energy storage density of 1.457 J/cm3 at 122 kV/cm and energy storage efficiency of 81.9%. [Display omitted] [ABSTRACT FROM AUTHOR]

Sr 2-2 x Ca 2 x CeO 4 (x = 0, 0.025, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) ceramics were synthesized through cold isostatic pressing and solid-state reaction. The microstructure, defects, microwave dielectric properties, and the effect of Ca2+ doping of Sr 2 CeO 4 ceramics were systematically investigated. As the sintering temperature increased, the densities of Sr 2 CeO 4 ceramics rose, the content of oxygen vacancies increased, and Ce4+ reduction would be enhanced. In addition, the Sr 2 CeO 4 structure had poor compatibility with Ca2+. The major phase could be kept unchanged only when x ≤ 0.1. The reason was that the doping of Ca2+ intensified the distortion of the CeO 6 octahedron and induced the structural transformation of the common edges (Sr 2 CeO 4) to the common angles (SrCeO 3). With the increase of dopant, the densities of Sr 2-2 x Ca 2 x CeO 4 ceramics increased significantly, while the content of oxygen vacancies also increased. The microwave dielectric properties were mainly influenced by the density, structural symmetry, defects, and the second phase SrCeO 3. The dielectric permittivity (ε r) of 13.4–15, the quality factor (Qf) of 118,580–52,170 GHz, and the temperature coefficient of resonant frequency (τ f) of −58.3 ∼ −47.5 ppm/°C were obtained for Sr 2-2 x Ca 2 x CeO 4 ceramics When x ≤ 0.1. This work has provided a foundation for further research on cerate microwave dielectric ceramics. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) has shown great development potential as a supercapacitor electrode material owing to both its high nitrogen content and good chemical stability. However, its specific capacitance remains limited by the poor electronic conductivity and low specific surface area. In this work, a novel ternary core–shell CS/CN/PPy nanocomposite was successfully fabricated via an in-air CVD method and an in situ polymerization route. Both the carbon spheres (CS) and polypyrrole (PPy) play an important role in improving the specific capacitance. Accordingly, the obtained CS/CN/PPy nanocomposite material achieved a high-level specific capacitance, which can reach 353.4 F g−1 at specific current of 1 A g−1. [ABSTRACT FROM AUTHOR]

In the application of graphitic carbon nitride photocatalytic hydrogen production, utilizing transition-metal sulfides instead of noble metals as cocatalysts has broad research prospects. Among them, nickel sulfide is favored by researchers due to its easy preparation, low cost, chemical stability, and excellent photocatalytic performance. Unfortunately, the strong sulfur–hydrogen bonds suppress its development. In this study, we successfully fabricated bimetallic CuNiSx quantum dots onto graphitic carbon nitride by the photochemical deposition method; such a small size can expose more active S sites on the edge. Simultaneously, the introduction of Cu2+ into NiSx can slightly modulate the electronic structure of Ni and S centers, thus weakening the sulfur–hydrogen bonds. Consequently, the average hydrogen evolution rate of CN/CuNiSx QDs achieved 1061 μmol h−1 g−1, which is 4.3 times than that of CN/NiSx QDs (246 μmol h−1 g−1). This research provides a new scenario to design bimetallic sulfide cocatalysts for H2 evolution. [ABSTRACT FROM AUTHOR]

A series of bismuth layer structured ferroelectrics (BLSFs) Bi 3- x (Li 0.5 Sm 0.5) x TiNbO 9 (abbreviated as BTNO-100 x LS, x = 0, 0.01, 0.02, and 0.03) high temperature piezoelectric ceramics were prepared by solid state reaction sintering. The microstructure, piezoelectric properties, and electrical conductivity of the sintered ceramics were studied systematically. The introduction of (Li 0.5 Sm 0.5)2+ ions does not change the bismuth layered structure obviously, but it will overmelt and affect its comprehensive properties with the increase of doping content. At last, the piezoelectric coefficient (d 33) of ∼9.6 pC/N and the Curie temperature (T c) is 921.3 °C, which shows good temperature stability and cycle stability, and the mechanical quality factor (Q m) reaches 2694.3 for x = 0.01 composition. These results show that BTNO-1LS is an excellent candidate for high temperature piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Electrostrictive materials are sought after in high-precision displacement actuators due to their ultra-low hysteresis electrostrain. Here we report a very promising electrostrictive material by doping barium zirconate into a sodium potassium niobate matrix. Also, the dielectric behaviors and electrostrictive properties of (1- x)K 0.5 Na 0.5 NbO 3 - x BaZrO 3 (x = 0.10, 0.12, 0.14 and 0.16) ceramics are investigated in details. The doping of barium zirconate allows the diffuse phase transition to occur near room temperature. Diffuse dielectric anomalies at high temperatures are observed in poled ceramics, which are closely related to the activation of defects. High electrostrain (∼0.1 %) with ultra-low strain hysteresis (< 12 %) are obtained at x = 0.14. Moreover, electrostrain exhibits excellent stability over a wide temperature range from 30 ℃ to 120 ℃.Further, the electrostrictive coefficient of ∼0.066 m4/C2 for the component was determined at high temperatures and high electric fields, demonstrating the excellent potential of the K 0.5 Na 0.5 NbO 3 -BaZrO 3 solid solutions as electrostrictive materials. [ABSTRACT FROM AUTHOR]

A series of lead-free (Bi 0·5 Na 0.5) 0.84 Sr 0·16 Ti 1- x (Y 0·5 Nb 0.5) x O 3 (abbreviated as BNST-100 x YN) relaxor ferroelectric ceramics were prepared by solid state reaction sintering. The micro morphology, dielectric properties, and energy storage properties of the ceramics with increasing doping content were systematically studied, and their conductive mechanism was also studied. The perovskite structure was not significantly changed with the addition of (Y 0·5 Nb 0.5)4+ complex ions, but it led to a certain amount of flake grains appear and element precipitation with increasing composition. And the larger dielectric breakdown strength (DBS) and lower remanent polarization (P r) were attained with the recoverable energy storage density (W rec) of ~1.0433 J/cm3 for x = 0.04 composition. In addition, it showed outstanding dielectric temperature stability and cycle stability. These results indicated that BNST-4YN ceramics are an excellent candidate for energy storage device and temperature-stable dielectric equipment. [ABSTRACT FROM AUTHOR]

In this work, (0.64- x)Bi 0.5 Na 0.5 TiO 3 - 0.36Sr 0.7 Bi 0.2 TiO 3 - x (K 0.5 La 0.5)(Ti 0.9 Zr 0.1)O 3 lead-free piezoceramics were designed and fabricated by a conventional solid-phase sintering process. It is found that large strains (0.33 %), low hysteresis coefficients (32 %), and large dynamic d 33 * (367 p.m./V) were obtained at x = 0.01. The large strain originates from the reversible transition of the relaxor to the long-range ferroelectric order in the electric field. When the ferroelectric and relaxor phases coexist in a proper ratio, they can provide a favorable condition for the easier movement of the domains and improve the strain properties. In addition, after 105 cycles, the bipolar strain loop of x = 0.01 content changed slightly, demonstrating excellent fatigue resistance. This work provides a new way to design piezoelectric ceramics with large strain and low hysteresis. [ABSTRACT FROM AUTHOR]

(1- x)[0.94(Bi 0.5 Na 0.5)TiO 3 -0.06BaTiO 3 ]- x Ba(Sn 0.70 Nb 0.24)O 3 (abbreviated as BNTBT-100 x BSN) lead-free ceramics were fabricated with a relative density greater than 96 %, and the structure as well as performance were tested. BNTBT-100 x BSN ceramics are pseudo-cubic perovskite structure, with dense surface morphology. Doping BSN can effectively reduce the dielectric loss of ceramics and increase the relaxation properties to a certain extent. The randomly distributed ferroelectric phase was replaced by polar nano regions, thereby improving the electro-strain and energy storage performance of the system. The largest electro-strain and the corresponding normalized strain (d 33 *) reach ~ 0.43 % and 633 pm/V respectively in the BNTBT-1BSN ceramic. The largest effective energy storage density reaching ~ 1.28 J/cm3 was tested in BNTBT-2BSN. BNTBT-100 x BSN ceramics provide a feasible idea for the systematic research of lead-free ferroelectrics and improvements in electro-strain and energy storage applications. [ABSTRACT FROM AUTHOR]

Lead-free antiferroelectric (AFE) ceramic materials have attached increasing attention in application of high-power capacitors for the past few years, due to their high energy storage density and environmental protection. However, the related applications are seriously restricted because of the limited number of environment friendly AFE candidate materials, high cost and low energy storage efficiency. In this work, the A-site ion Sm3+ doped 0.88NaNbO 3 -0.12Sr 0·7 Bi 0·2 TiO 3 lead-free AFE P phase ceramics (0.88Na 1-3 x Sm x NbO 3 -0.12Sr 0·7 Bi 0·2 TiO 3 , abbreviated as NN-SBT-100 x Sm) were prepared and characterized. With the increase of Sm doping amount, a relaxor-like behavior was found in the dielectric-temperature curves of NN-SBT-100 x Sm, indicating the AFE orthorhombic P phase is gradually replaced by an AFE orthorhombic R phase. As a result, double-like and slim P - E curve with near-zero residual polarization and suppressed hysteresis loss was obtained at x > 0.01. More encouragingly, a good discharge energy storage density (W rec = 3.58 J/cm3) and a high efficiency (η = 82%) at a low electric field (E = 200 kV/cm) has been recorded simultaneously for NN-SBT-2Sm relaxor AFE ceramic, which are better than the other lead-free energy storage ceramics under the same E. In addition, the energy storage properties of NN-SBT-2Sm ceramics exhibit outstanding temperature and frequency stability. These results indicate that NN-SBT-2Sm relaxor AFE ceramic has a great practical value in pulse power capacitors. [ABSTRACT FROM AUTHOR]

A series of Bi 0.5- x Er x Na 0.4 K 0.1 TiO 3 (BNKT- x Er) ceramics were designed and fabricated, the dopant effects on dielectric, piezoelectric and photoluminescence properties were studied. The results show that the piezoelectric property of BNKT can be enhanced by a trace amount of Er dopant, which is also reflected in the large linear electrostrain (S uni = 0.29%, under 55 kV/cm) achieved in BNKT-0.0025 Er. On the other hand, higher Er content can produce excellent dielectric temperature stability, with △ ԑ / ԑ 150 °C < ±15% over temperature range of 90∼510 °C. Meanwhile, all BNKT- x Er ceramics exhibit good photoluminescence properties, which may open new applications of these multifunctional ceramics. [ABSTRACT FROM AUTHOR]

• Three dielectric anomaly peaks were found in a two-layer BLSFs high temperature piezoelectric ceramic for the first time. • The contribution of each ion to the piezoelectric properties was analyzed by conclusion of Rietveld refinement. • (Y 0.5 Sb 0.5)4+-doped BTN ceramic have reduced oxygen vacancies and increased activation energy, resulting in enhanced ceramic performance at high temperature. Bismuth layered material stand out from other piezoelectric materials due to their high Curie temperature (T c) and are often used in high temperature piezoelectric actuators and capacitors. However, its low piezoelectric coefficient (d 33) and dielectric constants (ε′) limit the scope of application of this material. The Bi 3 Ti 0.99 (Y 0.5 Sb 0.5) 0.01 NbO 9 (BTN-1YSb) ceramics by solid state sintering method show improved d 33 (8.1 pC/N), dielectric constants (ε′ ∼2051), temperature stability (d 33 ＞8 pC/N at 800 °C) and mechanical quality factor (Q m ∼ 1834). After Rietveld refinement, it was found that the oxygen element contributed the most to the spontaneous polarization (P s) enhancement of the piezoelectric material. In addition, three dielectric anomalous peaks are observed for the first time in BTNO-4YSb BTN-3YSb ceramics, which is due to the interaction of point defects with domain walls in a wide temperature range. This advantage can be maximized by tuning the dielectric anomaly peak to provide a more stable d 33 at high temperatures. This study analyzes that the contribution of each ion to the piezoelectric properties of BTN-based ceramics and provides a good example for the study of dielectric peaks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tunable carbon vacancy g-C 3 N 4 is synthesized by wood pyrolysis induced etching. • CO x gas effectively tailors physicochemical and photoelectric properties of g-C 3 N 4. • Small particle sizes and amorphization transition in phase structure is achieved. • This photocatalyst exhibits nearly 20 times improvement in H 2 evolution. Post-thermal treatment is a widely employed technique for the fabrication of graphitic carbon nitride (g-C 3 N 4) with thin-layered, porous and defect-rich structures for photocatalytic hydrogen evolution. Here, the synthesis of catalysts is assisted with wood pyrolysis, which triggers an etching on g-C 3 N 4 by released trace carbon oxides gases. Specifically, a nickel foam is used as the substrate to hold a piece of pine wood on top of bulk g-C 3 N 4 , thereby preventing interfacial structural damage and introduction of impurities in a conventionally used solid state mixing process. Such a multicomponent atmosphere results g-C 3 N 4 with tunable carbon vacancies (TCCNx) and small particle sizes, and therefore a large specific surface area is obtained. The as-prepared TCCNx exhibits an improved photocatalytic hydrogen evolution rate of 3703 μmol·g−1·h−1, outperforming the bulk g-C 3 N 4 by ∼20 folds under visible light (λ > 420). The reason for enhanced photocatalytic performance is ascribed to a favorable optical property, rapid charge carrier separation, and efficient charge transfer processes. This unique top-down etching strategy provides valuable insights for designing efficient polymer photocatalysts with controllable properties. [ABSTRACT FROM AUTHOR]

The n-ZnO/n-SnO 2 nano-heterostructures surrounded by high-energy facets have been designed and synthesized via a simple two-stage route and used as functional materials of chlorine gas sensor. The composition, morphology and structure of ZnO–SnO 2 nano-heterostructures are characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). It is found that both the SnO 2 octahedra nanoparticles and the ZnO–SnO 2 nano-heterostructures are surrounded by high-energy (221) facets. The sensor with the ZnO–SnO 2 nano-heterostructure nanoparticles presents a much higher response (230.52) to Cl 2 (upgrade to 50 times) than that of the sensor with the pure SnO 2 nanoparticles. Moreover, a new and reasonable method is used to calculate the detection limit of two sensors. The sensor with 10% ZnO–SnO 2 sample (ZnO: SnO 2 = 10%, mol%) reveals lower detection limit (0.06 ppm) than that of pure SnO 2 sample (1.10 ppm). The superior Cl 2 sensing performance is closely related to the effects of the high-energy facets and the formation of energy barrier between ZnO and SnO 2. [ABSTRACT FROM AUTHOR]

Micrometre-sized pure BiFeO 3 (BF) and Ce-doped Bi 0.9 Ce 0.1 FeO 3 (BCF) powders were synthesized by using conventional hydrothermal (H) and microwave assisted hydrothermal (MH) methods. The BF-H and BCF-H show obviously enhanced weak ferromagnetic characteristic, in which the BCF-H exhibits excellent magnetic performance, with significantly increased maximum magnetization of ∼3.6 emu/g (under 50 kOe magnetic field) and remanent magnetization of ∼0.268 emu/g at room temperature. The superior magnetic property of BCF-H could be attributed to the suppression of spiral structure and the modulation of canting angle of spins in antiferromagnetic sublattices. [ABSTRACT FROM AUTHOR]

Dielectric ceramics for capacitors have attained significant attention in current time owing to their large power densities and fast charge/discharge rates. Lead-free [(Bi0.50Na0.40K0.10)0.94Ba0.06]1-xLaxTi0.975Ta0.025O3 (abbreviated as BNKBTT-100xLa) relaxor ceramics are prepared using mixed-oxide technique. All ceramics are revealed a pseudo-cubic structure using X-ray diffraction technique. The long-range order existing in BNKBTT-100xLa ceramics is found to reduce with increasing composition. As a result, a highly effective energy storage density (Wrec) ~ 1.558 J/cm3 and efficiency (η) ~ 88.46% is achieved in BNKBTT-2La ceramic. In addition, BNKBTT-2La composition is fatigue-free up to 105 cycles. Also, BNKBTT-4La ceramic exhibits a dielectric constant (ε') ~ 2281 near 150 °C with Δε'/ε'150 °C below 15% over a large range from 39 to 383 °C, showing an outstanding dielectric temperature stability. Therefore, BNKBTT-2La and BNKBTT-4La ceramics are outstanding for energy density and thermally stable dielectric permittivity, respectively, for the device applications. [ABSTRACT FROM AUTHOR]

In this study, (1- x)(0.66Bi 0.5 Na 0.5 TiO 3 –0.34Bi 0.2 Sr 0.7 TiO 3)– x K 0.5 Nd 0.5 TiO 3 (BNBST– x KNT) ceramics were designed and synthesized, and they present significantly enhanced dielectric temperature stability and energy storage properties. The BNBST–0.06KNT composition exhibits a remarkable dielectric stability, as reflected in its stable dielectric constant (△ ԑ / ԑ 150 °C < ±15%) over a broad temperature range (25–401 °C). BNBST–0.02KNT achieves a high energy storage density W rec = 1.2 J/cm3 under 110 kV/cm with an energy storage efficiency η of 76.9%, and the improved energy storage property originates from the improved breakdown field strength and decreased hysteresis behavior. The electrical conductivity and relaxation behaviors of BNBST– x KNT were also analyzed via impedance spectroscopy. [ABSTRACT FROM AUTHOR]

Lead-free perovskite materials for capacitors have been recognized worldwide attention in recent times with high storage energy density and efficiency. A series of (Bi0.50Na0.40K0.10)0.94Ba0.06Ti(1−x)(Al0.50Ta0.50)xO3 ceramics are synthesized using traditional mixed oxide route. All ceramics are in single-phase perovskite-like structure. At room temperature, high storage energy density, Wr ~ 1.67 J/cm3, and conversion efficiency, η ~ 81.46%, are perceived for x = 0.06 composition at 115 kV/cm. Temperature-dependent study obtains Wr ~ 1.21 J/cm3 and η ~ 84.96% at 80 °C with 80 kV/cm field. In addition, composition x = 0.06 is fatigue-free from 1 to 105 cycles measured at 80 kV/cm field. Furthermore, ceramic x = 0.04 is obtained a high bipolar strain ~ 0.31% at 80 kV/cm compared to other compositions. Hence, the compositions x = 0.06 for high energy density and x = 0.04 for strain might be useable in many electronic components. [ABSTRACT FROM AUTHOR]

A ternary solid solution of Bi 0.5 Na 0. 5 TiO 3 –Bi 0.5 K 0. 5 TiO 3 –Bi(Mg 2/3 Ta 1/3)O 3 (BNKT- x BMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT- x BMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (T F-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d 33 * = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase. [ABSTRACT FROM AUTHOR]

• Nonaqueous HEMA-DEGDA gelation system is developed to form Li-BASE green body. • Plasticizer is successfully used to eliminate cracks and warpage in the green body. • Perfect gelcast of Li-BASE is obtained with mechanical strength of 17 MPa. • Sintered gelcast of Li-BASE exhibits good mechanical and electrical properties. A novel non-aqueous gelcasting system based on the polymerization of 2-hydroxyethyl methacrylate (HEMA) with low toxicity is applied to the fabrication of lithium stabilized beta alumina solid electrolyte (Li-BASE). Triethanolamine and polyethylene glycol (MW. 1000) are used as dispersant and plasticizer, respectively. Effects of dispersant concentration, solids loading and plasticizer concentration on the rheological behavior of the suspensions are investigated and optimized. Cracking and warpage phenomena in the gelcast green body during drying process are discussed. Green body gelcast from the optimized suspension shows homogeneous microstructure with a relative density of 59.4 % and a bending strength of 17 MPa. Properties, including the relative density, phase composition, microstructure, bending strength and ionic conductivity, of Li-BASEs sintered from green body formed by gelcasting and cold isostatic press are evaluated. Results show that gelcasting forming technique performs well in preparing BASE ceramics with high Weibull modulus and ionic conductivity. [ABSTRACT FROM AUTHOR]

The high storage energy density (W rec) and conversion efficiency (η) for lead-free ceramics have been attained significant interest in recent times for electronic devices. Enhanced W rec and stable fatigue properties are examined for lead-free 0.94Bi 0·50 (Na 0·78 K 0.22) 0.50 Ti 1- x (Al 0·50 Nb 0.50) x O 3 -0.06BaZrO 3 (for 0 ≤ x ≤ 0.05) ceramics, synthesized using the solid-state reaction method. Crystal structure and lattice dynamics are revealed by the X-ray diffraction and Raman scattering techniques. Highly compact ceramics is obtained with decreasing average grain size from 0.94 ± 0.23 μm (for x = 0) to 0.76 ± 0.31 μm (for x = 0.05) as a function of composition. A high W rec ~1.32 J/cm3 and η ~76.60% is achieved for x = 0.04 ceramic at room temperature with applied 95 kV/cm. In addition, W rec ~1.40 J/cm3 and η ~86% are perceived with a 90 kV/cm at 80 °C. Also, it is obtained as a fatigue-free property for x = 0.04 composition ceramic up to 105 cycles. Hence, this improvement in energy density performance and stable fatigue resistance for x = 0.04 dielectric ceramic is expected for practical applications in many electronic appliances. [ABSTRACT FROM AUTHOR]

(1- x)[(Na 0.5 Bi 0.5) 0.84 Sr 0.16 ] 0.98 La 0.01 TiO 3 - x K 0.5 Na 0.5 NbO 3 (abbreviated as NBSLT-100 x KNN) lead-free perovskite relaxor ferroelectric ceramics are synthesized through the conventional solid-state reaction. The effects of KNN on the ceramic polycrystalline structure, dielectric temperature stability, and energy-storage characteristics are studied systematically. All samples exhibit a single perovskite structure and compact surface morphology. Thermally stable dielectric permittivity (ε ′) is obtained from 62 to 331 °C range for NBSLT-5KNN ceramic with ε ′ ~ 2286 at 150 °C less than ± 10% fluctuation rate. The addition of KNN refines the hysteresis loops and gradually increases the dielectric breakdown strength, which endows NBSLT-5KNN ceramic with the best energy-storage performance compared to other compositions. A high effective energy-storage density (W rec) ~ 1.234 J/cm3 with efficiency (η) ~ 74.7% are acquired at 90 kV/cm. The energy-storage performance is revealed an excellent fatigue resistant stability. Hence, the introduction of KNN makes NBSLT-5KNN ceramic an outstanding competitor for energy-storage equipment applications. [ABSTRACT FROM AUTHOR]

Graphite carbon nitride (g-C 3 N 4) is an appealing metal-free photocatalyst for hydrogen evolution, but the potential has been limited by its poor visible-light absorption and unsatisfactory separation of photo-induced carriers. Herein, a facile one-pot strategy to fabricate carbon self-doped g-C 3 N 4 composite through the calcination of dicyanamide and trace amounts of dimethylformamide is presented. The as-obtained carbon self-doped catalyst is investigated by X-ray photoelectron spectroscopy (XPS), confirming the substitution of carbon atoms in original sites of bridging nitrogen. We demonstrate that the as-prepared materials display remarkably improved visible-light absorption and optimized electronic structure under the premise of principally maintaining the tri- s -triazine based crystal framework and surface properties. Furthermore, the carbon doped g-C 3 N 4 composite simultaneously weakens the transportation barrier of charge carriers, suppresses charge recombination and raises the separated efficiency of photoinduced holes and electrons on account of the extension of pi conjugated system. As a result, carbon self-doped g-C 3 N 4 exhibits 4.3 times greater photocurrent density and 5.2 times higher hydrogen evolution rate compared with its bulk counterpart under visible light irradiation. [ABSTRACT FROM AUTHOR]

Energy density and fatigue resistance properties were investigated for lead-free Na 0.46 Bi 0.46 Ba 0.05 La 0.02 Zr 0.03 Ti 0.97- x Sn x O 3 (for 0 ≤ x ≤ 0.15) ceramics, synthesized via solid-state reaction technique. Perovskite pseudo-cubic crystal structure was revealed for all ceramics using X-ray diffraction. Polarization and current density versus electric field were perceived and suggested the relaxor behavior with increasing composition. A high storage energy density ~1.58 J/cm3, and conversion efficiency ~71.7% at ~110 kV/cm applied field was obtained for x = 0.03 composition at room temperature. Energy storage density was revealed ~1.53 J/cm3, and efficiency ~88.6% at 110 °C with a 100 kV/cm applied field. In addition, ceramic x = 0.03 was fatigue-free from 1 to 105 cycles. Hence, the composition x = 0.03 might be applicable for high energy storage devices. [ABSTRACT FROM AUTHOR]

The sodium ion intercalated ultrathin δ‐MnO2 flakes (abbreviated as NaxKMO) are synthesized by one‐step hydrothermal synthesis. Benefiting from the synergistic effect of sodium ion intercalating process and the homogeneous few‐layered microstructure, the NaxKMO electrode shows increased electron conduction as well as largely enhanced intercalation capacitive performance of 324.2 F g−1 at 0.5 A g−1 and 40.91 % capacitance retention at 8 A g−1 is obtained. Meanwhile, the 91.9 % diffusion contribution for NaxKMO electrode is clarified to be higher than that of KMO electrode, which indicates the preintercalated sodium ions caused a promoted diffusion‐controlled kinetic in charge‐discharge processes for the NaxKMO electrode. An asymmetric supercapacitor device (ASC) is assembled with the NaxKMO cathode and activated carbon anode. With a voltage window of 1.6 V, the fabricated ASC device delivers a high energy and power densities of 31.2 Wh kg−1 and 1571 W kg−1, respectively. With the continuous charge‐discharge tests, the device demonstrates outstanding capacitance retention of 98.2 % after 5000 cycles at 1 A g−1, suggesting a great potential of sodium ion intercalated MnO2 film electrodes in practical applications. [ABSTRACT FROM AUTHOR]

0.94(Bi 0.5 Na 0.5)(Y 0.5 Ta 0.5) x Ti 1- x O 3 -0.06BaTiO 3 lead-free piezoelectric ceramics were prepared by a conventional solid-state reaction method to study their excellent electro-strain properties and energy storage characteristics systematically. All ceramics exhibited a dense surface morphology. The introduction of (Y 0.5 Ta 0.5)4+ complex ions destroyed the long-range ferroelectric order, which reduced the T F-R to the operating temperature, resulting in an easier field-induced transition between relaxor and ferroelectric phase. Therefore, for x = 0.01 component attained unipolar strain of 0.37% under 52 kV/cm, and the corresponding normalized strain d 33 * was 708 pm/V. Besides, the destruction of the ferroelectric phase also induced a pinched hysteresis loop and the maximum storage density of 1.215 J/cm3 with the efficiency of 68.7% obtained at 98 kV/cm for BNYT30 ceramics. These all demonstrated that the doping of complex ions (Y 0.5 Ta 0.5)4+ made the BNT-BT an outstanding candidate for actuators and energy storage devices. [ABSTRACT FROM AUTHOR]

Polycrystalline (1- x)[(Na 0.5 Bi 0.5) 0.95 Ba 0.05 ] 0.98 La 0.02 TiO 3 - x K 0.5 Na 0.5 NbO 3 systems were prepared using the solid-state reaction technique. Modification of (Na 0.5 Bi 0.5) 0.95 Ba 0.05 ] 0.98 La 0.02 TiO 3 ceramic with a proper amount of K 0.5 Na 0.5 NbO 3 can effectively improve the temperature-stable of dielectric properties. A variation in dielectric constant is maintained smaller than ±5% from 80 to 300 °C accompanied with a low dielectric loss (≤0.04). The relaxor properties of the doped samples are significantly enhanced. A high energy storage density of 1.1 J/cm3 and efficiency ~80% at 90 kV/cm are achieved in the x = 0.05 composition. Hence, the as-prepared ceramics might be practical in dielectric constant which can work stably at a high temperature range and pulsed capacitors. [ABSTRACT FROM AUTHOR]

This work reports the existence of double polarization hysteresis (P – E) loop in Aurivillius-phase ferroelectric Bi 4 Ti 3 O 12 (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P – E loop is recalled by Nb donor doping, and associated composition Bi 4 Ti 2.97 Nb 0.03 O 12.015 (BiT-0.03Nb) shows high remnant polarization (P r = 12.5 μC/cm2) and large field-induced strain (S 33 = 5.6 × 10−4). In addition, this doping results in bulk conductivity (σ b) of BiT decreasing dramatically and associated activity energy (E a) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg2+ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ˜0.65 × 10−2 S cm−1 in the bulk. [ABSTRACT FROM AUTHOR]

A novel (0.67- x)BiFeO 3 -0.33BaTiO 3 - x (K 0.5 Nd 0.5)TiO 3 (KNT100 x , x = 0.0, 0.02, 0.04, 0.06, 0.08 mol%) ceramics were fabricated and their microstructure and electrical properties were studied. All samples displayed a pseudo-cubic symmetry, and adding of KNT had little effect on grain size. The dielectric analysis displayed the dispersion increases with the addition of KNT compositions, showing strong relaxor properties. Besides, high dielectric constant (ε') of 23000 and dielectric peak temperature (T m) of 390 °C remain at 1 kHz in the x = 0.02 sample while the dielectric loss (tanδ) dropped below 0.5 in the range of 30–400 °C, showing excellent electrical insulation performance. In addition, doping of KNT had obvious influence on the strain, and a large strain (Smax) of 0.26% was obtained at x = 0.02 due to the increase of electrical insulation. More importantly, the strain at 50 kV cm−1 enhanced significantly with temperature increasing, reaching a maximum strain of 0.75% with a small hysteresis coefficient of 30% at 110 °C. Particularly, KNT02 exhibited excellent fatigue resistance within 105 fatigue cycles. Presumably these results are attributed to the coexistence of ferroelectric and non-ergodic relaxor domains and the thermally activated domain wall motion. [ABSTRACT FROM AUTHOR]

A NiCo-LDH/Mn 3 O 4 composite is synthesized on nickel foam substrate though a two-step electrodepositon process. The growth of Mn 3 O 4 nanoneedles on NiCo-LDH nanosheets can greatly reduce the transport pathway of electrons and ions. Meanwhile, abundant active sites for redox reactions are generated and the structural endurance together with chemical stability of material is improved, thus strongly enhancing the electrochemical characteristics. When measured in a typical three-electrode cell, NiCo-LDH/Mn 3 O 4 demonstrates a high specific capacity of 1.86 C cm−2 (1034.33 C g−1) at the current density of 1 mA cm−2, a superior rate capability of maintaining 76.88% at 20 mA cm−2 and 17.98% capacity loss after 5000 cycles. In addition, an all-solid-state hybrid supercapacitor device (HSC) is fabricated with NiCo-LDH/Mn 3 O 4 as the cathode and commercially-used active carbon as the anode, which delivers a superior energy density of 57.03 Wh kg−1 at the power density of 765.8 W kg−1 and maintains 20.98 Wh kg−1 even when the power density increases to 9681.6 W kg−1. Therefore, the satisfactory electrochemical property enables NiCo-LDH/Mn 3 O 4 to become a prospective electrode material in energy storage field. • We first synthesize a 3D partially-cladding NiCo-LDH/Mn 3 O 4 composite. • The integration of nanosheets and nanoneedles improves the stability. • We first define and use the curve of accumulative contribution versus potential. • The NiCo-LDH/Mn 3 O 4 //AC HSC device shows high energy density and power density. [ABSTRACT FROM AUTHOR]

Low frequency dielectric dispersion behavior of the indium doped cadmium zinc telluride single crystal has been investigated. The temperature dependent of dielectric loss shows a broadening peak at high temperatures, which is attributed to thermally activated relaxation process. The large dielectric permittivity can be attributed to the influence of the dc conductivity and the predominance of the dc conduction in low frequency region overshadows the true behavior of the imaginary part of dielectric permittivity. The contribution of dc conduction and ac conduction has also been studied. A polaron theory indicates that the dielectric relaxation of the indium doped cadmium zinc telluride crystal at high temperature is associated with the hopping localized cadmium vacancies and telluride antisites defects. The hopping energy increases from 1.204 eV at 499 K to 1.267 eV at 534 K monotonically, which is close to the thermal activation energy 1.541 eV and dc conductivity activation energy 1.239 eV. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics SrBi2-xLaxNb2O9 (SBLNO) were prepared by a solid state reaction process. X-ray diffraction analysis indicated that single phase layered perovskites were obtained. The maximum dielectric permittivity peak broadened gradually with the lanthanum content increasing indicated that the phase transition from normal ferroelectrics to relaxorlike ferroelectrics occurs in SBLNO. The modified Curie–Weiss (CW) law was used to describe the relaxor behavior of SBLNO ceramics. The relaxation indication coefficient (γ) was estimated from a quadratic fit of modified CW law and was found to be 1.71 and 1.72 for SBLN20 and SBLN30 specimens, respectively. The substitution of La3+ ions for Bi3+ ions in the Bi2O2 layers resulted in a shift in the Curie point to lower temperature and an increase in remanent polarization and electrical field-induced strain. The maximum strain for SBLN30 specimen was found to be about 2.5×10-5 at the 5 MV/m. The nature of relaxor behavior of SBLNO is attributed to the cationic disordering at nanoscale on A site by the La3+ substituted Bi3+ of Bi2O2 layers. [ABSTRACT FROM AUTHOR]

The temperature and frequency dependences of dielectric properties of barium strontium titanate [Ba0.85Sr0.15TiO3 (BST15)] ceramics have been investigated. The dielectric relaxation behavior above 180 °C was observed in BST15 ceramics with broad dielectric peaks. The contribution of dc conduction and universal dielectric response to the relaxation has been studied. In contrast to typical ion conductor such as La2Mo2O9, the extent of dielectric dispersion shows the similar temperature dependence characteristic. Polaron theory indicates that the relaxation in BST15 ceramics at high temperatures is associated with the hopping localized oxygen vacancies. [ABSTRACT FROM AUTHOR]

The temperature dependence of dielectric permittivity was investigated for the barium zirconium titanate solid solution system [BZT, Ba(ZrxTi1-x)O3 0.25≤x≤0.5]. The dielectric relaxation behavior was observed in these ferroelectrics with diffused phase transition. In contrast to the canonical relaxors such as Pb(Mg1/3Nb2/3)O3, the diffused phase transition of BZT could not be well described by the popular modified Curie–Weiss law. Quasiferroelectric state theory was introduced to explain the dielectric results of the BZT relaxors. [ABSTRACT FROM AUTHOR]

Dielectric properties, microstructures, and phase transition behaviors of α and β phases of CaxBa1-xNb2O6 (x=0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345 °C) compared with Sr1-xBaxNb2O6. The α phase exhibits unambiguously a diffused phase transition, while the β phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1-xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates. [ABSTRACT FROM AUTHOR]

The leakage of raw material triethylamine in the process of chemical production causes harm and damage to health and environment. Therefore, the development of triethylamine sensors with high response and selectivity is urgently needed. Using metal organic frames (MOF) as templates has become a new strategy to prepare nano structural metal oxides based gas sensing materials, which leads to a high specific surface area and enhanced gas sensing performances. In this work, the metal organic framework MOF-5 decorated with large Ag particles is prepared by a conventional one-step solvothermal method. Then 3D ZnO/Ag micro-octahedra assembled from ZnO nanosheets are derived by subsequent calcination. The 3D ZnO/Ag micro-octahedra based sensor exhibits excellent gas sensing performance toward triethylamine, including an ultrahigh response of 293.8–10 ppm and selectivity, as well as a low operating temperature of 200 °C, and long-time stability. The excellent triethylamine gas sensing performance can be attributed to the synergy effect between oxygen vacancies and the catalytic spillover effect generated by the noble metal silver. This work shows that MOF derived hierarchical 3D ZnO/Ag micro-octahedra provides a great potential for triethylamine monitoring. • A novel MOF template method is used for facile and large-scale synthesis of 3D ZnO/Ag micro-octahedra. • The 3D ZnO/Ag micro-octahedra shows an ultrahigh response and excellent selectivity to TEA. • Ag particles lead to noble metal catalytic spillover effect and form Schottky junctions with ZnO. [ABSTRACT FROM AUTHOR]

Triethylamine is a kind of volatile organic compounds, which is harmful and toxic to the environment and people. Therefore, triethylamine gas sensors are increasingly demanded in practical applications. In this work, we synthesized the nitrogen-doped ZnO yolk-shell microspheres with mesoporous distribution by a facile strategy of hydrothermal-annealing. The influence of the amount of hexamethylene tetramine on the morphology of yolk-shell ZnO was studied and the yolk-shell ZnO (YSZ-3) prepared with 0.3 g hexamethylene tetramine showed the best gas sensing performances for triethylamine at 370 ℃. The response to 100 ppm triethylamine was 133. Moreover, a low triethylamine detection limit was achieved (1 ppm), with a response value of 2.6. The prepared yolk-shell ZnO showed an excellent selectivity to triethylamine, over ethanol, methanol, acetone, formaldehyde, ammonia, and toluene. Furthermore, YSZ-3 offered a low theoretical detection limit (42.4 ppb) and a fast response and recovery (20 s/5 s). Finally, the growth mechanism and gas sensing mechanism of yolk-shell ZnO were discussed. • The nitrogen-doped yolk-shell ZnO microspheres was synthesized by a hydrothermal-annealing method with HMTA assisted. • The special yolk-shell ZnO was prepared at micron-sized with the mesoporous distribution. • YSZ-3 with the maximum BET and best TEA sensing performance was obtained with 0.3 g HMTA. • The prepared YSZ-3 shows a low detection limit, good selectivity, fast response and recovery, and stability. • The growth mechanism and gas sensing mechanism of yolk-shell ZnO microspheres are discussed. [ABSTRACT FROM AUTHOR]

The perovskite structure of Pb(Zn[sub 1/3]Nb[sub 2/3])O[sub 3] (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb(Zr[sub 0.47]Ti[sub 0.53])O[sub 3] (PZT) across the morphotropic phase boundary (MPB). The 0.5 PZN–0.5 PZT specimen was found to have a two-phase zone, having a high piezoelectric coefficient, d[sub 33] (430 pC/N), an electromechanical coupling factor, k[sub p] (0.67), a field-induced strain, S (0.24% at 2 kV/mm), and a remnant polarization, P[sub r] (27 μC/cm2). A phase transition from a rhombohedral to tetragonal phase occurred when a relatively low electrical field was applied to the specimen. This transformation occurred only when the rhombohedral phase coexisted with an equal amount of the tetragonal phase of the perovskite structure. Small rhombohedral domains, which were present around the relatively large tetragonal domains, transformed as a result of the applied field. The excellent electromechanical properties at the MPB composition are attributed to this phase transition in the PZN based ceramics. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The high temperature capacitors operated in some harsh conditions require dielectric ceramics with stable permittivity, low dielectric loss and high resistivity to temperatures above 200 °C. In this work, high temperature dielectrics based on (1-x-y)Bi 0.5 Na 0.5 TiO 3 -xBiAlO 3 -yK 0.5 Na 0.5 NbO 3 ceramics were designed and prepared. The introduction of BiAlO 3 leads to the reduction of dielectric loss due to the formation of defect dipoles. And the introduction of K 0.5 Na 0.5 NbO 3 leads to the disruption of long-range ferroelectric order, which is helpful to increase the temperature stability of permittivity. The composition of x = 0.07 and y = 0.05 has a stable permittivity between 86.5 °C and 324.5 °C and dielectric loss below 0.02 in the temperature range of 110 °C–336 °C. Therefore, this system will be one of promising candidates of dielectrics used for high-temperature capacitors. [ABSTRACT FROM AUTHOR]